This invention relates to a power control circuit for a high intensity discharge lamp, for example of the type used in video displays. Typical liquid crystal display (LCD) and liquid crystal on silicon (LCOS) television (TV) projection systems utilize high-intensity discharge lamps (also referred to as bulbs) as image back lighting sources. High intensity discharge lamps typically operate with mercury vapor. Applying power to a partially energized mercury vapor lamp is to be avoided. Applying power to the lamp before the mercury vapor de-energizes, i.e., re-striking the lamp, shortens the lamp's life. To avoid this problem, some projection systems introduce a delay between power off and power on. This delay is sometimes referred to as a “restart” delay. The restart delay prevents a user from applying power to the television receiver until the mercury vapor lamp is substantially fully de-energized. An example of a typical restart delay time is approximately 30 seconds. Introducing a restart delay in this manner can be annoying to a user. Users have come to expect instant restart of their television sets since instant response is typical with television receivers that do not employ high-intensity discharge lamps. A typical high intensity discharge lamp can take approximately 30 seconds for the bulb to cool down and approximately another 30 seconds for the bulb to reheat.
Therefore a need exists for circuits and methods for applying power to such systems in a way that minimizes user perception of delay while preserving the life of the mercury vapor lamp.